Transient liquid phase material bonding and sealing structures and methods of forming same

ABSTRACT

A bonding element includes a first transient liquid phase (TLP) bonding element including a first material and a second material, the first material having a higher melting point than the second material, a ratio of a quantity of the first material and the second material in the first TLP bonding element having a first value and a second TLP bonding element including the first material and the second material, a ratio of a quantity of the first material and the second material in the second TLP bonding element having a second value different from the first value.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §120 as aContinuation-In-Part of U.S. application Ser. No. 14/815,098, titled“MULTILAYERED TRANSIENT LIQUID PHASE BONDING,” filed Jul. 31, 2015,which claims priority under 35 U.S.C. §119(e) to U.S. ProvisionalApplication Ser. No. 62/031,824, titled “COATED GRAIN TRANSIENT LIQUIDPHASE SOLDER,” filed on Jul. 31, 2014. The application also claimspriority under 35 U.S.C. §119(e) to U.S. Provisional Application Ser.No. 62/264,422, titled “SEAL RING,” filed on Dec. 8, 2015. Each of theseapplications is herein incorporated by reference in its entirety.

BACKGROUND

1. Field of Invention

Aspects and embodiments of the present invention are directed tometallization and/or bonding of electrical or electronic devicecomponents and/or components of packages for same.

2. Discussion of Related Art

In the art of electrical and electronic device fabrication and assembly,it is often desirable to make a substrate or surface (for example, acircuit board, ceramic monolithic microwave integrated circuit (MMIC)substrate, etc.) conductive. It is also often desirable to bond anelectrical or electronic component to a substrate or to bond componentsof a package for an electronic component with a thermally and/orelectrically conductive material. Processes for forming such conductivesurfaces or bonds can face a number of challenges, for example, cost,the use of high temperatures incompatible with other process steps,difficulty in filling of hollow features of a substrate, and/oroutgassing of byproducts incompatible with other process steps.

SUMMARY

In accordance with an aspect of the present invention, there is provideda bonding structure. The bonding structure includes a first layer offirst alloy component disposed on a substrate and a first layer of asecond alloy component disposed on the first alloy component. The secondalloy component has a lower melting temperature than the first alloycomponent. A second layer of the first alloy component is disposed onthe first layer of the second alloy component and a second layer of thesecond alloy component is disposed on the second layer of the firstalloy component.

In some embodiments, the bonding structure further comprises a thirdlayer of the first alloy component disposed on the second layer of thesecond alloy component.

In some embodiments, the bonding structure further comprises a firstbarrier layer configured to seal a surface of the second layer of thesecond alloy component from atmosphere and suppress oxidation of thesurface of the second layer of the second alloy component. The barrierlayer may include one or more of titanium, platinum, nickel, indiumoxide, and tin.

In some embodiments, the bonding structure further comprises interfacialbarrier layers disposed at interfaces between each layer of the firstalloy component and each layer of the second alloy component, thebarrier layers configured to suppress inter-diffusion of the first alloycomponent and the second alloy component. The interfacial barrier layersmay include one or more of titanium, platinum, nickel, indium oxide, andtin.

In some embodiments, the first alloy component and the second alloycomponent are selected to inter-diffuse and form an alloy when thebonding structure is heated to a temperature above the meltingtemperature of the second alloy component and below the meltingtemperature of the first alloy component.

In some embodiments, a quantity of the first alloy component and aquantity of the second alloy component in the bonding structure areselected to form an alloy having a melting temperature between themelting temperature of the first alloy component and the meltingtemperature of the second alloy component.

In some embodiments, the first alloy component is gold and in someembodiments, the second alloy component is indium.

In some embodiments, the first alloy component and the second alloycomponent are a pair of components selected from the pairs of componentsincluding aluminum and germanium, gold and silicon, gold and tin, copperand tin, lead and tin, and indium and tin.

In some embodiments, an electronic component package is hermeticallysealed with the bonding structure.

In some embodiments, an electronic device includes at least onecomponent bonded to the substrate with the bonding structure. Theelectronic device may include at least one electrical contact inelectrical communication with an electrical contact of the substrate viathe bonding structure.

In accordance with another aspect, there is provided a method of forminga wireless device. The method comprises forming at least one moduleincluding a substrate having a radio frequency circuit and at least onedevice bonded to a portion of the radio frequency circuit with a firstbonding structure. The first bonding structure includes a first layer offirst alloy component disposed on a substrate, a first layer of a secondalloy component disposed on the first alloy component, the second alloycomponent having a lower melting temperature than the first alloycomponent, a second layer of the first alloy component disposed on thefirst layer of the second alloy component, and a second layer of thesecond alloy component disposed on the second layer of the first alloycomponent.

In some embodiments, the at least one device is one of a poweramplifier, a low noise amplifier, and an antenna switch module.

In some embodiments, the method further comprises hermetically sealingthe at least one device in a package with a second bonding structureincluding a first layer of first alloy component disposed on asubstrate, a first layer of a second alloy component disposed on thefirst alloy component, the second alloy component having a lower meltingtemperature than the first alloy component, a second layer of the firstalloy component disposed on the first layer of the second alloycomponent, and a second layer of the second alloy component disposed onthe second layer of the first alloy component.

In some embodiments, the method further comprises forming an electricalconnection between at least one electrical contact of the at least onedevice and at least one electrical contact of the radio frequencycircuit with the first bonding structure.

In some embodiments, the method further comprises forming a transceiverand an antenna each in electrical communication with the at least onemodule.

In accordance with another aspect, there is provided a method of bondinga first assembly to a second assembly. The method comprises providing afirst assembly including a first binary component layer disposed on afirst substrate and providing a second assembly including a first layerof a first binary component disposed on a substrate, a first layer of asecond binary component disposed on the layer of the first binarycomponent, the second binary component having a lower meltingtemperature than the first binary component, a second layer of the firstbinary component disposed on the first layer of the second binarycomponent, and a second layer of the second binary component disposed onthe second layer of the first binary component. The method furthercomprises aligning the second assembly against the first assembly,heating the first assembly and second assembly to a temperature that isgreater than a melting point of the second binary component but lessthan the melting point of the first binary component, and maintainingthe temperature for a time sufficient for the layers of the first binarycomponent to inter-diffuse with the layers of the second binarycomponent to form an alloy from the first binary component and thesecond binary component.

In accordance with another aspect, there is provided a method of forminga bonding structure on a substrate. The method comprises forming a firstbinary component layer on the substrate, forming a first barrier layeron the first binary component layer, and forming a second binarycomponent layer on the first barrier layer. The first barrier layerincludes a material that suppresses diffusion of the second binarycomponent into the first binary component layer. The method furthercomprises forming a second barrier layer on the second binary componentlayer, forming another first binary component layer on the secondbarrier layer, forming a third barrier layer on the another first binarycomponent layer, forming another second binary component layer on thethird barrier layer, and forming a fourth barrier layer on the anothersecond binary component layer. The fourth barrier layer includes amaterial that suppresses diffusion of oxygen from the atmosphere intothe another second binary component layer.

In some embodiments, forming the second binary component layer comprisesdepositing material having a lower melting temperature than the firstbinary component on the first barrier layer.

In some embodiments, forming the second binary component layer comprisesdepositing material that will inter-diffuse with the first binarycomponent to form an alloy upon heating of the bonding structure abovethe melting temperature of the second binary component.

In some embodiments, a quantity of the first binary component in thefirst binary component layer and in the another first binary componentlayer and a quantity of the second binary component in the second binarycomponent layer and in the another second binary component layer areselected so that the alloy has a melting temperature between the meltingtemperature of the first binary component and the melting temperature ofthe second binary component.

In some embodiments, the method further comprises forming a furtherfirst binary component layer on the fourth barrier layer.

In some embodiments, depositing the first binary component layercomprises depositing a layer of gold on the substrate.

In some embodiments, depositing the second binary component layercomprises depositing a layer of indium on the first barrier layer.

In some embodiments, forming at least one of the first barrier layer,the second barrier layer, and the third barrier layer comprisesdepositing a layer of one or more of titanium, platinum, nickel, indiumoxide, and tin.

In accordance with another aspect, there is provided a solder materialcomprising a plurality of coated grains, each grain including a core anda coating layer, the core and the coating layer selected to provide atransient liquid phase for the solder material.

In some embodiments, the core and the coating layer include materialscapable of forming an alloy upon application of heat to the soldermaterial. The coating layer material may have a melting temperature thatis lower than a melting temperature of the core material. Theapplication of heat may result in the coating layer being heated to atemperature greater than the melting temperature of the coating layermaterial but less than the melting temperature of the core material, tothereby liquefy the coating layer and allow the liquefied coating layermaterial to diffuse into the core material. The coating layer and thecore may be dimensioned such that substantially all of the liquefiedcoating layer material is diffused into the core material to form thealloy.

In some embodiments, the alloy is electrically conductive. The corematerial may include gold. The coating layer material may includeindium.

In some embodiments, each grain further includes an outer layerimplemented on the coating layer, the outer layer configured to preventor reduce oxidation of the coating layer. The outer layer may includegold.

In some embodiments, each grain further includes a barrier layerdisposed between the coating layer and the core, the barrier layerconfigured to prevent or reduce premature diffusion between the coatinglayer and the core. The barrier layer may include titanium.

In accordance with another aspect, there is provided a method forfabricating a solder material. The method comprises forming or providinga plurality core particles and coating each of the core particles with acoating layer to yield a coated grain, the coated grain having atransient liquid phase property.

In accordance with another aspect, there is provided a method forforming a conductive alloy. The method comprises providing a soldermaterial that includes a plurality of coated grains, each grainincluding a core and a coating layer, the core and the coating layerselected to provide a transient liquid phase for the solder material,heating the solder material to a temperature that is between meltingtemperatures of the coating layer and the core, the melting temperatureof the coating layer less than the melting temperature of the core suchthat the coating layer becomes liquefied, and maintaining the heatinguntil a substantial amount of the liquefied coating layer diffuses intothe core to thereby form an alloy.

In some embodiments, the alloy has a melting temperature that issignificantly higher than the temperature of the coating layer.

In accordance with another aspect, there is provided a method forforming a conductive feature on a substrate. The method comprisesforming or providing a suspension of a plurality of coated grains in asolution, each grain including a core and a coating layer, the core andthe coating layer selected to provide a transient liquid phase property,dispensing the suspension onto the substrate, evaporating at least someof the solution, heating the coated grains to a temperature that isbetween melting temperatures of the coating layer and the core, themelting temperature of the coating layer less than the meltingtemperature of the core such that the coating layer becomes liquefied,and maintaining the heating until a substantial amount of the liquefiedcoating layer diffuses into the core to thereby form a conductive alloy.

In some embodiments, the dispensing includes spin coating, spraying, orscreen printing.

In some embodiments, the substrate includes a semiconductor wafer or apackaging substrate. The packaging substrate may include a laminatesubstrate or a ceramic substrate. The ceramic substrate may include alow-temperature co-fired ceramic substrate.

In some embodiments, the conductive feature is a conductive pad or aconductive trace. The conductive feature may be a conductive layerconfigured to provide radio-frequency (RF) shielding functionality. Theconductive layer may include a conformal conductive layer.

In accordance with another aspect, there is provided a packagedradio-frequency (RF) module. The packaged RF module comprises apackaging substrate that includes a ground plane, one or more componentsmounted on the packaging substrate, and a conductive layer implementedover the one or more components, the conductive layer electricallyconnected to the ground plane to provide RF shielding functionality forat least some of the one or more components, the conductive layerincluding an alloy resulting from heating of a solder material, thesolder material including a plurality of coated grains, each grainincluding a core and a coating layer, the core and the coating layerselected to provide a transient liquid phase for the solder material.

In some embodiments, the packaged RF module further comprises anovermold encapsulating the one or more components, the conductive layerdisposed on an upper surface of the overmold.

In some embodiments, at least some of the conductive layer is formeddirectly on the one or more components.

In some embodiments, the conductive layer further covers one or moresides of the packaging substrate so as to yield a conformal coveragealong with the portion over the one or more components.

In accordance with another aspect, there is provided a method of forminga conductive feature on a semiconductor die. The method comprisesdepositing a layer of conductive material on the die using a coatingmaterial structure including a first layer of first alloy component, afirst layer of a second alloy component disposed on the first alloycomponent, the second alloy component having a lower melting temperaturethan the first alloy component, a second layer of the first alloycomponent disposed on the first layer of the second alloy component, anda second layer of the second alloy component disposed on the secondlayer of the first alloy component, and patterning the layer ofconductive material.

In accordance with another aspect, there is provided a method of formingan electronic component module including a substrate having anelectrical circuit. The method comprises bonding at least one device toa portion of the electrical circuit with a bonding structure including afirst layer of a first alloy component disposed on the substrate, afirst layer of a second alloy component disposed on the first alloycomponent, the second alloy component having a lower melting temperaturethan the first alloy component, a second layer of the first alloycomponent disposed on the first layer of the second alloy component, anda second layer of the second alloy component disposed on the secondlayer of the first alloy component.

In accordance with another aspect, there is provided a bonding element.The bonding element comprises a first transient liquid phase structureincluding a first material and a second material, the first materialhaving a higher melting point than the second material, a ratio of aquantity of the first material and the second material in the firsttransient liquid phase structure having a first value and a secondtransient liquid phase structure including the first material and thesecond material, a ratio of a quantity of the first material and thesecond material in the second transient liquid phase structure having asecond value different from the first value.

In some embodiments, the bonding element further comprises a thirdtransient liquid phase structure including the first material and thesecond material, a ratio of a quantity of the first material and thesecond material in the third transient liquid phase structure having athird value, the third value being between the first value and thesecond value.

In some embodiments, one of the first value, the second value, and thethird value is selected such that one of the first transient liquidphase structure, the second transient liquid phase structure, and thethird transient liquid phase structures forms an intermetallic alloyhaving a melting point higher than a melting point of the secondmaterial responsive to being heated above the melting point of thesecond material.

In some embodiments, the first transient liquid phase structure isdisposed on a substrate and surrounds a device disposed on thesubstrate. The second transient liquid phase structure may surround thefirst transient liquid phase structure. At least one transient liquidphase strut may connect the first transient liquid phase structure andthe second transient liquid phase structure. One of the first transientliquid phase structure and the second transient liquid phase structuremay be configured to direct molten liquid escaping from the one of thefirst transient liquid phase structure and the second transient liquidphase structure away from the device. One of the first transient liquidphase structure and the second transient liquid phase structure may beconfigured to direct molten liquid escaping from the one of the firsttransient liquid phase structure and the second transient liquid phasestructure toward the other of the first transient liquid phase structureand the second transient liquid phase structure.

In accordance with another aspect, there is provided a bonding element.The bonding element comprises a first bonded element including a firstalloy of a first material and a second material, the first materialhaving a higher melting point than the second material, a ratio of aquantity of the first material and the second material in the firstbonded structure having a first value, and a second bonded elementincluding a second alloy of the first material and the second material,a ratio of a quantity of the first material and the second material inthe second bonded element having a second value different from the firstvalue.

In some embodiments, one of the first alloy and the second alloy is astoichiometric intermetallic alloy of the first material and the secondmaterial. One of the first bonded element and the second bonded elementmay include a region richer in the second material than thestoichiometric intermetallic alloy.

In some embodiments, the bonding element hermetically seals a devicewithin a cavity. The device may be a radio frequency (RF) device.

In some embodiments, the bonding element is included in a radiofrequency (RF) device module. The bonding element may be included in aRF device.

In some embodiments, the bonding element is disposed on a contact pad ofa device and provides an electrical connection from an external circuitto the contact pad.

In some embodiments, an electronic device includes at least onecomponent bonded to a substrate with the bonding element. The electronicdevice may include at least one electrical contact in electricalcommunication with an electrical contact of the substrate via thebonding element.

In accordance with another aspect, there is provided a method of forminga wireless device. The method comprises forming at least one moduleincluding a substrate having a radio frequency circuit and at least onedevice bonded to a portion of the radio frequency circuit with a bondingelement. The bonding element includes a first bonded element including afirst alloy of a first material and a second material, the firstmaterial having a higher melting point than the second material, a ratioof a quantity of the first material and the second material in the firstbonded element having a first value and a second bonded elementincluding a second alloy of the first material and the second material,a ratio of a quantity of the first material and the second material inthe second bonded element having a second value different from the firstvalue.

In accordance with another aspect, there is provided a method of forminga wireless module including a device and a substrate. The methodcomprises forming a first bonding element on a surface of one of thedevice and the substrate, the first bonding element including a firstalloy of a first material and a second material, the first materialhaving a higher melting point than the second material, a ratio of aquantity of the first material and the second material in the firstbonding element having a first value, forming a second bonding elementon a surface of one of the device and the substrate, the second bondingelement including a second alloy of the first material and the secondmaterial, a ratio of a quantity of the first material and the secondmaterial in the second bonding element having a second value differentfrom the first value, contacting the device with the substrate with thefirst bonding element and the second bonding element disposed betweenthe device and the substrate and in contact with both the device and thesubstrate, and heating the first bonding element and the second bondingelement at a temperature and time sufficient for the first material andthe second material in the first bonding element and the second bondingelement to interdiffuse and form a first bonded element and a secondbonded element.

In some embodiments, the device is one of a power amplifier, a low noiseamplifier, and an antenna switch module.

In some embodiments, the ratio of the quantity of the first material andthe second material in the first bonded element is determined by adistance between the first bonded element and a third bonded element.

In accordance with another aspect, there is provided a method of formingat least one bonding structure. The method comprises forming a firstbonding element on a first portion of a substrate. The first bondingelement includes a first material and a second material. An amount ofthe first material and an amount of the second material are present inthe first bonding element in a first ratio. The method further includesforming at least one second bonding element on a second portion of thesubstrate. The at least one second bonding element includes the firstmaterial and the second material. The amount of the first material andthe amount of the second material are present in the at least one secondbonding element in a second ratio different from the first ratio. Thefirst bonding element and the at least one second bonding element areheated to form the at least one bonding structure, the at least onebonding structure consisting essentially of a substantiallystoichiometric alloy of the first material and the second material.

In some embodiments, forming the first bonding element includes formingthe first bonding element with a protrusion of a one of the firstmaterial and the second material having a higher melting temperaturethan the other of the first material and the second material, theprotrusion configured to direct molten material from the first bondingelement toward the second bonding element.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 illustrates a pair of substrates bonded to one another;

FIG. 2 illustrates a substrate conformally coated with a conductivematerial layer;

FIG. 3 illustrates an alloy system in accordance with an embodiment;

FIG. 4 illustrates a temperature profile utilized in embodiments of abonding, sealing, or coating method;

FIG. 5 illustrates embodiments of a structure for a use in performing abonding, sealing, or coating method;

FIG. 6 illustrates another embodiment of a structure for a use inperforming a bonding, sealing, or coating method;

FIG. 7 illustrates another embodiment of a structure for a use inperforming a bonding, sealing, or coating method;

FIG. 8A illustrates an embodiment of a group of structures for a use inperforming a bonding, sealing, or coating method at a first stage in themethod;

FIG. 8B illustrates the embodiment of the group of structures of FIG. 8Aat a second stage in the method;

FIG. 8C illustrates the embodiment of the group of structures of FIG. 8Aat a third stage in the method;

FIG. 9A illustrates another embodiment of a structure for a use inperforming a bonding, sealing, or coating method;

FIG. 9B illustrates another embodiment of a structure for a use inperforming a bonding, sealing, or coating method;

FIG. 9C illustrates another embodiment of a structure for a use inperforming a bonding, sealing, or coating method;

FIG. 10 illustrates a flowchart of an embodiment of a method for formingan embodiment of a structure for a use in performing a bonding, sealing,or coating method;

FIG. 11A illustrates an embodiment of a structure for a use inperforming a bonding, sealing, or coating method after a first act ofthe method of FIG. 10;

FIG. 11B illustrates the structure for a use in performing the bonding,sealing, or coating method after a second act of the method of FIG. 10;

FIG. 12 illustrates an embodiment of a method of applying embodiments ofa structure for a use in performing a bonding, sealing, or coatingmethod on an object;

FIG. 13A illustrates a suspension of embodiments of a structure for ause in performing a bonding, sealing, or coating method;

FIG. 13B illustrates the suspension of FIG. 13A being applied to anobject;

FIG. 14A illustrates a wafer upon which embodiments of structures for ause in performing a bonding, sealing, or coating method may be applied;

FIG. 14B illustrates application an embodiment of structures for a usein performing a bonding, sealing, or coating method to the wafer of FIG.14A;

FIG. 14C illustrates features of a device formed on the wafer of FIG.14A with the embodiment of the structures for use in performing thebonding, sealing, or coating method;

FIG. 15A illustrates a device bonded to a substrate with an embodimentof a structure or method disclosed herein;

FIG. 15B illustrates a substrate coated with an electrically conductivefilm with an embodiment of a structure or method disclosed herein;

FIG. 15C illustrates another substrate coated with an electricallyconductive film with an embodiment of a structure or method disclosedherein;

FIG. 15D illustrates another substrate coated with an electricallyconductive film with an embodiment of a structure or method disclosedherein;

FIG. 15E illustrates a via formed in a substrate and coated with anelectrically conductive film with an embodiment of a structure or methoddisclosed herein;

FIG. 15F illustrates a via formed in a substrate and filled with anelectrically conductive material with an embodiment of a structure ormethod disclosed herein;

FIG. 16A is a plan view of an embodiment of package including ahermetically sealed device;

FIG. 16B is a cross section of the package of FIG. 16A.

FIG. 17A illustrates an embodiment of a device bonded to a substratewith an embodiment of a structure or method disclosed herein;

FIG. 17B illustrates a cross section of the device and substrate of FIG.17A;

FIG. 18A illustrates an embodiment of a device electrically coupled to asubstrate with an embodiment of a structure or method disclosed herein;

FIG. 18B illustrates a cross section of the device and substrate of FIG.18A;

FIG. 19 illustrates a first portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 20 illustrates a second portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 21 illustrates a third portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 22 illustrates a fourth portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 23A illustrates a first portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 23B illustrates a second portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 23C illustrates a third portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 23D illustrates a fourth portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 24A illustrates a first portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 24B illustrates a second portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 24C illustrates a third portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 25A illustrates a first portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 25B illustrates a second portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 25C illustrates a third portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 26A illustrates a first portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 26B illustrates a second portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 26C illustrates a third portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 27A illustrates a first portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 27B illustrates a second portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 27C illustrates a third portion of an embodiment of a method ofbonding a first assembly to a second assembly;

FIG. 28 illustrates a flowchart of an embodiment of a method for forminga bonding structure on a substrate;

FIG. 29 illustrates a flowchart of an embodiment of another method forforming a bonding structure on a substrate;

FIG. 30 illustrates a flowchart of an embodiment of a method for bondinga first assembly to a second assembly;

FIG. 31 illustrates a flowchart of another embodiment of a method forbonding a first assembly to a second assembly;

FIG. 32 illustrates an embodiment of a bonding structure including twoportions and a bonded structure resulting from bonding the two portions;

FIG. 33A illustrates another embodiment of a bonding structure includingtwo portions and a bonded structure resulting from bonding the twoportions;

FIG. 33B illustrates an embodiment of the configuration of the twoportions of FIG. 33A;

FIG. 33C illustrates another embodiment of the configuration of the twoportions of FIG. 33A;

FIG. 34A illustrates another embodiment of a bonding structure includingtwo portions and a bonded structure resulting from bonding the twoportions;

FIG. 34B illustrates an embodiment of the configuration of the twoportions of FIG. 34A;

FIG. 34C illustrates another embodiment of the configuration of the twoportions of FIG. 34A;

FIG. 35A illustrates another embodiment of a bonding structure includingtwo portions and a bonded structure resulting from bonding the twoportions;

FIG. 35B illustrates an embodiment of the configuration of the twoportions of FIG. 35A;

FIG. 35C illustrates another embodiment of the configuration of the twoportions of FIG. 35A;

FIG. 36A illustrates an embodiment of plurality of bonding structuresand a metal film prior to bonding;

FIG. 36B illustrates the bonding structures of FIG. 36A after bonding tothe metal film;

FIG. 37A is a plan view of an embodiment of a hermetically sealedpackage;

FIG. 37B is a cross sectional view of the package of FIG. 37A;

FIG. 38 illustrates another embodiment of a bonding structure includingtwo portions and a bonded structure resulting from bonding the twoportions;

FIG. 39 is a plan view of another embodiment of a bonding structure;

FIG. 40 illustrates an embodiment of an electronics module; and

FIG. 41 illustrates an embodiment of a wireless device.

DETAILED DESCRIPTION

This invention is not limited in its application to the details ofconstruction and the arrangement of components set forth in thefollowing description or illustrated in the drawings. The invention iscapable of other embodiments and of being practiced or of being carriedout in various ways. Also, the phraseology and terminology used hereinis for the purpose of description and should not be regarded aslimiting. The use of “including,” “comprising,” “having,” “containing,”“involving,” and variations thereof herein is meant to encompass theitems listed thereafter and equivalents thereof as well as additionalitems.

Disclosed herein are examples related to transient liquid phase (TLP)surface coating and bonding. In some embodiments, transient liquid phasesurface coating or bonding is achieved through an application of asuspension of grains having a plurality of layers, followed by heatingto cause the surface coating or bonding. In other embodiments, transientliquid phase surface coating or bonding is achieved through anapplication of a film having a plurality of layers to or between one ormore surfaces, followed by heating to cause the surface coating orbonding. The resulting surface coating or bond can be used to, forexample, join components, make a surface conductive, provide conductivepaths within hollow features of a structure, etc. For example, in someembodiments, a transient liquid phase bonding process may be used toform a structure 10 as illustrated in FIG. 1 having a first substrate orcomponent 12 bonded to a second substrate or component 16 with a layerof bonding material 14. In various embodiments, one or both of thesubstrates or components 12, 16 are active substrates, for example,semiconductor material substrates that may include one or more activedevices. In other embodiments, one or both of the substrates orcomponents 12, 16 may be mounting substrates, for example printedcircuit boards or components of a package for an electronic device.

In some embodiments, a transient liquid phase surface coating processmay be utilized to form a structure 20 as illustrated in FIG. 2 havingan electrically conductive coating 28 bonded to an upper surface 24 of asubstrate 22. The electrically conductive coating conformally covers theupper surface 24 of the substrate 22 and fills rough surface featuresand/or recesses, for example, recess 26. Like substrates 12 and 16 ofFIG. 1, in various embodiments substrate 22 is one or more of an activesemiconductor substrate, a mounting substrate, for example, a printedcircuit board, or a component of a package for an electronic device.

In the following disclosure aspects and embodiments of transient liquidphase bonding are discussed. It is to be understood that the materials,structures, and techniques disclosed with respect to transient phaseliquid bonding may also be applicable to processes of transient liquidphase surface coating and/or package sealing. Transient liquid phase(TLP) bonding is a multistage process whereby a multi-component system,for example, two metals capable of forming a binary alloy, are broughtinto contact, heated above the melting point of the component materialhaving a lower melting point than the other component material, thenheld at a temperature for a time adequate for the two materials tointer-diffuse, thereby making the binary alloy. In some embodiments, aTLP bonding structure may include three or more components. For example,either the grain structures or the layered structures may be formed withat least one layer (or a core in embodiments of the grain structures)formed of an alloy of more than one material. Non limiting examples ofTLP bonding structures utilizing more than two materials includestructures utilizing gold and a lead-tin alloy and structures utilizinggermanium and an aluminum-copper alloy. In some embodiments, where thealloy is the component material having a lower melting point than theother component material, the alloy may be a eutectic alloy.

In some embodiments, it has been found desirable to achieve trueliquefaction of the lower melting temperature material. This providesfor the resulting bond interface to effectively overcome challenges to agood bond, for example, device topology, surface roughness, etc.

It is also desirable to have the liquefaction of the lower melting pointmaterial occur since the diffusion of the lower melting pointcomponent(s) into the higher melting point component in a liquid phaseis typically orders of magnitude faster than solid state inter-diffusionof the lower and higher melting point materials.

If the materials are chosen correctly and the fractions of the low andhigh melting temperature components are chosen appropriately, the lowmelting temperature component layer can be fully alloyed with the highmelting temperature component. The resulting alloyed structure can thenhave a higher melting point than that used to create the bond since allof the low melting temperature component has been alloyed by diffusioninto a more refractory mix.

One binary system that is used as an example in this disclosure is theindium-gold system, with the indium being the lower melting temperaturecomponent. There are many other binary TLP component systems which willbehave similarly and this disclosure is not limited to only TLPstructures and methods involving the indium-gold system.

Depending on the materials used, an intermetallic between the binarycomponents can undesirably form even at room temperature, or duringheating to the melting point of the low melting temperaturecomponent—but prior to liquefaction of the low melting temperaturecomponent. Premature intermetallic formation can undesirably consumesome or all of the low melting temperature component such that theliquefaction is less effective at conformally coveringtopology/roughness within the bond area.

For this reason, rather thick layers of the low melting temperaturematerial have been used in the past to ensure that, despite ongoing lowtemperature diffusion, there is sufficient thickness of the lowtemperature melting component remaining when the TLP structure reachesthe melting point of the low melting temperature component.

Using these thicker layers of low melting temperature component canrequire one to bond for longer times to complete the inter-diffusion ofcomponents during the bonding process due to the longer length scalerequired for atoms to move by diffusion.

In addition, thicker low melting temperature component layers have beenknown to be easier to “squeeze out” when the bonding process reaches themelting point and force is applied to make the bond.

Thus, a TLP material system is desirable that may be utilized to form astructure that won't prematurely alloy, will alloy quickly and/orcompletely during bonding, and won't squeeze out during the bondingprocess.

In some implementations, transient liquid phase bonding is a multistageprocess utilizing a multi-component system, for example, a binary alloy34 that includes a first component material 30 and a second componentmaterial 32 (FIG. 3). The first component material 30 and the secondcomponent material 32 may both be metals. The first component material30 and second component material 32 are brought into contact at a firsttemperature (T, see FIG. 4) below the melting point of both the firstcomponent material 30 (for example, T1, illustrated in FIG. 4) and themelting point of the second component material 32 (for example, T2,illustrated in FIG. 4). The two component materials 30, 32 are heated toa temperature above the melting point of the component material 30, 32having a lower melting point (T1) than the other component material 30,32. The two component materials 30, 32 are then held at a temperaturefor a time adequate for the two component materials 30, 32 tointer-diffuse, for example, for the lower melting point material todiffuse into the higher melting point material, thereby making the alloy34.

A significant advantage of a transient liquid phase bond is that theresulting alloy can have a higher melting point than the temperatureused to make the bond. This is due to inter-diffusion of the constituentcomponents resulting in an alloy having a higher melting point than thelower melting point material, and in some instances a melting pointbetween the melting point of the lower melting point material and themelting point of the higher melting point material.

In some embodiments, and as an example, a multi-component systemincludes a plurality of grains where indium (In, melting point of 156.6degrees C.) is used as a coating layer outside of a gold (Au, meltingpoint of 1,064 degrees C.) core lying within the interior of each grain.The low melting point constituent such as indium can be selected to wetand bond well to the chosen application site or substrate, and/or toother grains.

A plurality of such layered grains to be alloyed can, for example, beplaced in a volatile liquid to form a suspension which is disposed on asubstrate by spin coating, spraying, or screen printing. The liquidnature of the suspension can provide advantageous features such as lowapplication/processing cost, a low processing temperature, conformalfilling of recessed features, etc.

Preparation of the foregoing suspension can include preparing grains ofa high melting point material coated with a low melting point materialthat inter-diffuses with the high melting point material, therebyresulting in a high melting point alloy. This can be achieved, forexample, through sol gel preparation followed by electro-less coating.Alternatively, preparation of such grains can include spray powderformation, traditional ball milling, or other methods of small grainproduction.

In some embodiments, an additional layer of a non-oxidizing material(for example, another layer of gold) can be formed over the indium layerto prevent or reduce oxidation of the indium before bonding.

In some applications, use of a diffusion barrier between low and highmelting point materials can prevent or reduce premature diffusionalloying before the material is heated with the intent to drive reactionto a refractory alloy. In the foregoing grain structure example, anintermediate coating of the diffusion barrier layer can be providedbetween the low and high melting point materials to prevent or reducetheir premature inter-diffusion.

The foregoing grains and applications of such grains (for example, insuspension) can provide a number of advantages. For example, a resultingnetwork would not have flux or residual organic material to burn off aswith other alternative epoxy based methods of application. In anotherexample, one does not need to rely on mechanical contact in a matrix forconductivity such as in an application using simple metallic particlesuspension. In yet another example, the grains having one or morefeatures as described herein can be diffusion soldered to any metal thatreadily alloys with the system.

In some implementations, one can extend one or more of the features asdescribed herein to yield a porous conducting network capable of beingassembled at relatively low temperature with the appropriate choice of,for example, grain sizes and coating thicknesses. One can also utilizeone or more features of the present disclosure to configure a systemhaving more than a binary functionality. One can also utilize one ormore features of the present disclosure to configure grain cores thatare non-conducting and/or non-alloying, if desired.

FIG. 5 illustrates grains 100 having cores 102 and coating layers 104 soas to form a binary system. In some embodiments, the size of the core102 (for example, diameter d1, d2, or d3) and/or the thickness of thecoating layer 104 (for example, thickness t1, t2, or t3) can be selectedfor a particular application. Such selected core dimensions and coatinglayer thickness can be average values or be in some ranges. For example,the core dimensions and coating layer thickness may be selected suchthat on average, the relative amounts of core material and coatingmaterial in the population of grains are sufficient to form an alloyhaving a higher melting temperature than the coating material when thegrains are fully alloyed.

In some embodiments, materials for the core 102 and the coating layer104 of the grain 100 are selected to yield a binary alloying system. Insome embodiments, the coating layer material is selected to have a lowermelting temperature than that of the core material. Further, an alloyresulting from the coating layer 104 and the core 102 can have a meltingtemperature that is significantly higher than the melting temperature ofthe coating layer material. In various examples described herein, thecore 102 is described as being gold (Au, melting point of 1,064 degreesC.), and the coating layer 104 is described as being indium (In, meltingpoint of 156.6 degrees C.). However, it will be understood that othercombinations of materials can also be utilized. Examples of othermaterial systems that may be used in various embodiments disclosedherein include, but are not limited to, aluminum (Al, melting point of660 degrees C.)-germanium (Ge, melting point of 938 degrees C.)(eutectic alloy melting point of 450 degrees C.), Au-silicon (Si,melting point of 1,414 degrees C.) (eutectic alloy melting point of 363degrees C.), Au-tin (Sn, melting point of 232 degrees C.) (eutecticalloy melting points of 217 degrees C. (93.7% Sn) and 278 degrees C.(29% Sn)), copper (Cu, melting point of 1,085 degrees C.)-Sn (eutecticalloy melting point of 270 degrees C.), lead (Pb, melting point of 327degrees C.)-Sn (eutectic alloy melting point of 183 degrees C.), andIn—Sn (eutectic alloy melting point of 120 degrees C.). Alloys of thesematerials having compositions other than the eutectic compositions havehigher melting points than the eutectic compositions. At least somealloys of these materials have melting temperatures higher than that ofthe component with the lower melting temperature. For ease ofdescription, aspects and embodiments disclosed herein are described asincluding alloying components of Au and In, however, it should beunderstood that any one or more of these other alloy systems may besubstituted for the Au—In system.

FIG. 6 shows that in some embodiments, a grain 100 having a core 102 anda coating layer 104 may further include an outer layer 106 configuredto, for example, prevent or reduce oxidation of the coating layer 104.Such an outer layer can be formed from, for example, gold. The outerlayer 106 is sufficiently thin, while providing the foregoing protectivefunctionality, to allow the coating layer 104 to be heated. In someembodiments an outer layer 106 that is only a few nanometers thick, forexample, less than about 10 nanometers thick provides adequateprotection against oxidation of the coating layer 104. As describedherein, once heated appropriately, the outer layer 106 and the core 102can form an alloy with the coating layer 104.

In the foregoing example, the outer layer 106 is described as having thesame material as the core 102. However, it will be understood that theouter layer 106 can be formed from material that is different than thecore 102. For example, in some embodiments, the outer layer 106 may beformed of one or more materials including, but not limited to, titanium(Ti) platinum (Pt), nickel (Ni), indium oxide (In₂O₃), tin (Sn), orcombinations or alloys of same.

FIG. 7 shows that in some embodiments, a grain 100 having a core 102 anda coating layer 104 may further include a barrier layer 108 disposedbetween the core 102 and the coating layer 104. Such a barrier layer canbe configured to, for example, prevent or reduce prematureinter-diffusion between the core 102 and the coating layer 104. Forexample, if an indium coating layer 104 is put in direct contact with agold core 102, intermetallic diffusion can occur even at roomtemperature within each grain. Using a diffusion barrier layer 108 suchas titanium (Ti) can prevent such premature inter-diffusion, and yet notinterfere with the desired inter-diffusion upon the indium liquefying.By way of an example, a titanium layer having a thickness in a range of200 Å-400 Å can be disposed between the indium layer and the gold coreto prevent or reduce the premature alloying of the indium layer and thegold core. Other materials that may be utilized for the barrier layerinclude platinum (Pt), nickel (Ni), indium oxide (In₂O₃), tin (Sn), andcombinations or alloys of same.

FIGS. 4 and 8A-8C illustrate an example of an alloying process that canbe implemented utilizing grains such as those described with referenceto FIGS. 5-7. FIG. 4 shows a temperature profile 50 as a function oftime as the grains (for example, applied in suspension form) are heated.FIGS. 8A-8C illustrate example states at various stages of such aheating process.

In an unheated state 120, a plurality of grains 100 are shown to form anetwork (FIG. 8A). Such a network can be formed by, for example,application of the grains 100 in a suspension form on surfaces and/orfeatures of a substrate. As described herein, the grains 100 are shownto have their respective cores 102 and coating layers 104. In such anunheated state, the temperature of the grains 100 is shown to be T, andthe coating layers are in un-melted form.

When the network of grains 100 are heated to a temperature that isgreater than the melting temperature T1 of the coating layer materialbut less than the melting temperature T2 of the core material, thecoating layers 104 are shown to be liquefied in state 130 (FIG. 8B).Such liquefied material 132 of the coating layers 104 is shown to flowbetween neighboring grains. In such a heated state, the liquefiedcoating layer material 132 diffuses into the core material.

When the foregoing heating temperature is maintained for a timesufficient to allow the foregoing diffusion, an alloyed state 140 (FIG.8C) can result. In such a state, alloyed grains 142 are shown to form anetwork. Such an alloyed network is shown to have a melting temperatureT3 that is significantly higher than the melting temperature T1 of thecoating layer 102 material. In the example shown, the meltingtemperature T3 of the network of alloyed grains 142 is shown to be lessthan the melting temperature T2 of the core material.

In the context of the example indium-gold binary system, the meltingtemperature T3 of the resulting alloy varies, depending on the relativeamounts of the indium and gold. When the percent weight of indium in thebinary system is zero, the system is essentially gold, and its meltingtemperature is approximately 1,064 degrees C. As the percent weight ofindium increases, the melting temperature of the resulting alloydecreases, and reaches a valley of about 458 degrees C. when the indiumcontent is about 25% by weight. As the percent weight of indiumincreases further, the melting temperature of the resulting alloyincreases and reaches a peak value of about 510 degrees C. when theindium content is about 37% by weight. As the percent weight of indiumincreases further, the melting temperature of the resulting alloydecreases and reaches a valley value of about 495 degrees C. when theindium content is about 42% by weight. As the percent weight of indiumincreases further, the melting temperature of the resulting alloyincreases and reaches a peak value of about 541 degrees C. when theindium content is about 54% by weight. As the percent weight of indiumincreases further, the melting temperature of the resulting alloydecreases to the melting temperature of approximately 156.6 degrees C.when the indium content is 100% by weight.

Based on the foregoing examples, one can see that there is a large rangeof melting temperatures of the indium-gold alloy (for example, less than50% of indium by weight) that is significantly higher (for example,greater than or equal to about 458 degrees C.) than the meltingtemperature of indium (156.6 degrees C.). In some embodiments, theamount of indium in the grains (and therefore in the alloy) can beselected based on factors such as the foregoing increased meltingtemperature (of the alloy), an electrical property of the alloy, amechanical property of the resulting alloy network, and/or the alloyingprocess.

In the context of the example grains having gold cores and indiumcoating layers, and as described in reference to FIGS. 5-7, the indiumcontent can be varied by, for example, varying the coating layerthickness t1, t2, t3 relative to the core diameter d1, d2, d3. When thethickness of the indium coating layer is in a desired range (for a givendiameter of the gold core), there can be sufficient amount of indium fora relatively quick diffusion process into the gold core withoutsignificant amount of excess indium. Accordingly, the coating layerthickness t1, t2, t3 and/or the core diameter d1, d2, d3 can be adjustedto preferably yield such an alloying process. It will be understood thatsuch thickness and diameter values or ranges can be average values orranges among the grains.

It is noted that if there is insufficient amount of indium (for example,due to the coating layer being too thin), a layer of alloy can form inthe cores, and the alloying process can self-terminate when theliquefied indium runs out. In such a situation, the inner portions ofthe cores can remain as highly conductive gold. If the heating processis continued for a long time, the indium can be driven further into thecore; however, such a lengthy process may not be desirable in a quickand low-temperature alloying process.

It is also noted that if there is too much indium (e.g., due to thecoating layer being too thick), the resulting alloy can have higherresistivity. In some applications, such higher resistivity of the alloymay or may not be desirable. Further, there may be excess indium that isnot diffused into the core, thereby resulting in indium reflow. In sucha situation, the excess indium having relatively high resistance canundesirably melt and reflow at relatively low temperature during asubsequent process step involving heating.

In the various examples described in reference to FIGS. 5-8C, the grains100 are depicted as being generally spherical. FIGS. 9A-9C show thatgrains 100 having one or more features as described herein do notnecessarily need to have spherical shapes. FIG. 9A is a spherical shapedexample grain 100 similar to the examples described in reference toFIGS. 5-8C. FIG. 9B shows an example grain 100 that has a generallyrounded shape (for example, an ellipsoid), but not a spherical shape. Asdescribed herein, such a grain can include a core portion 102 and acoating layer portion 104.

FIG. 9C shows that in some embodiments, a grain 100 does not necessarilyneed to have a rounded shape, and can include one or more sharp featuressuch as corners. The example grain 100 of FIG. 9C is shown to have apolygonal sectional shape. As described herein, such a grain can includea core portion 102 and a coating layer portion 104. It will beunderstood that grains having one or more features as described hereincan have other shapes than those illustrated. Further, it will beunderstood that non-spherical grains may also include coating layers 104as illustrated in FIG. 6 and/or barrier layers 108 as illustrated inFIG. 7.

FIG. 10 illustrates a process 150 that can be implemented to manufacturecoated grains having one or more features as described herein. FIGS. 11Aand 11B shows example states of such a process.

In block 152, core particles are provided or formed. In FIG. 11A, one ofsuch core particles is depicted at 102. In block 154, coating layers areformed on the core particles. In FIG. 11B, a coating layer 104 isdepicted as being formed on the core particle 102.

FIG. 12 shows a process 160 that can be implemented to apply grainshaving one or more features as described herein. FIGS. 13A and 13B showexample states of such a process.

In block 162, a suspension of coated grains is formed in a solution. InFIG. 13A, such a suspension is depicted at 170, where coated grains 100are suspended in a solution 172. In block 163, the suspension can beapplied. In FIG. 13B, the suspension 170 is depicted as being dispensed(arrow 176) from a dispensing apparatus 174 onto a substrate 178.

FIG. 14A shows that in some implementations, a substrate on which theforegoing suspension of coated grains is applied can be a semiconductorwafer 178. Such an application can be achieved by, for example, a spinapplication where the wafer 178 is spun while the suspension is appliedat or close to the center of the wafer 178. Due to the spinning 180 ofthe wafer 178, the suspension on the wafer 178 migrates outward (arrows182).

FIG. 14B shows a side view of the spin application example of FIG. 14A.By way of an example the suspension can be sprayed 186 from a dispensingapparatus 188 onto a center portion of a surface 184 of the wafer 178.Such sprayed suspension can then move outward due to the spinning of thewafer 178.

In some embodiments, a wafer can include an array of units 190 that willbecome individual die when singulated. FIG. 14C shows an example of sucha unit 190, where conductive features, for example, contact pads 192 andconductive traces 194 can be formed from patterning of a conductivelayer formed as described herein utilizing the coated grains. In otherembodiments, the conductive layer is formed from an embodiment of alayered bonding structure as described below, for example, withreference to FIGS. 26A-26C or 27A-27C. Such conductive features areexamples of features formed on a surface. In some embodiments, thecoated grains can also be used to fill or coat 3-dimensional featuressuch as vias, recesses, side walls, etc., in substrates such as wafers,packaging substrates (for example, laminate substrates and ceramicsubstrates), and circuit boards. Examples of such applications aredescribed in greater detail below.

FIGS. 15A-15F illustrate non-limiting examples of conductive featuresthat can be formed using coated grains having one or more features asdescribed herein. As described herein, such conductive features can beutilized to join parts together, to form a conductive path or layer, orany combination thereof.

In an example configuration 200 of FIG. 15A, a conductive layer 204 canbe utilized to mount a component 206 (for example, a die, surface mounttechnology (SMT) device, etc.) on a substrate 202 (for example, apackaging substrate). To achieve such a mounting, a layer of un-alloyedgrains can be formed on the substrate 202, followed by positioning ofthe component 206. The assembly can then be heated to a low temperaturethat is higher than the melting temperature of the coating layer asdescribed herein, to thereby form an alloy layer between the substrate202 and the component 206.

In an example configuration 210 of FIG. 15B, a conductive layer 214 isformed on an underlying structure 212. By way of a non-limiting example,the structure 212 can be an overmold structure implemented on apackaging substrate, and such a conductive layer 214 can be utilized asa radio-frequency (RF) shield. Such a conductive layer can beelectrically connected to a ground plane within the packaging substrate(not shown) through, for example, shielding wirebonds, a conductivecomponent, a conductive layer on one or more of the side walls, or anycombination thereof.

FIGS. 15C and 15D show examples where conductive layers formed asdescribed herein can conform to three dimensional surfaces. In anexample configuration 220 of FIG. 15C, a conductive layer 224 formedwith coated grains as described herein can conform to a recess 226defined by a structure 222. Such a structure can be, for example, anovermold structure formed over a packaging substrate. By way of anexample, the recess 226 can be formed on the upper surface of theovermold structure to expose an upper surface of a component (not shown)configured to provide an electrical connection between its upper surfaceand the packaging substrate (for example, to a ground plane therein).Once such an upper surface is exposed, the conductive layer 224 can beformed, and such a layer can conform to the contour of the upper surfaceof the overmold structure and the recess 226. In some embodiments, sucha conformal conductive layer 224 can be utilized as an RF shield.

In an example configuration 230 of FIG. 15D, a conductive layer 234formed with coated grains as described herein can conform to an uppersurface and side surfaces of a package 232. Such a package can include,for example, a combination of an overmold and a packaging substrate,with one or more components mounted on the packaging substrate andencapsulated by the overmold. In some embodiments, a box shaped modulehaving such a conformal conductive layer 234 can cover five of the sixsides, except the bottom side (which is used to mount to, for example, acircuit board). Such a conformal conductive layer 234 can beelectrically connected to a ground plane within the packaging substratethrough, for example, conductive features that are exposed to theuncoated side walls. In some embodiments, the packaging substrate can bea laminate substrate or a ceramic substrate such as a low-temperatureco-fired ceramic (LTCC) substrate. In some embodiments, the upperportion of such a packaging substrate can include an overmold structure(such as in the example of FIG. 15D). In other embodiments, theconformal conductive layer can also cover components and featureswithout an overmold structure, as well as the side walls of thepackaging substrate.

FIGS. 15E and 15F show examples where coated grains having one or morefeatures as described herein can be utilized to form conductive vias. Inan example configuration 240 of FIG. 15E, a via 246 formed between upperand lower sides of a substrate 242 (for example, a wafer, one or morelayers of a packaging substrate, etc.) can be made conductive byformation of a layer 244 resulting from alloying of the coated grains asdescribed herein. In an example configuration 250 of FIG. 15F, a via 256between upper and lower sides of a substrate 252 (for example, a wafer,one or more layers of a packaging substrate, etc.) can be filled withconductive material resulting from alloying of the coated grains asdescribed herein.

In some embodiments, a method of transient liquid phase bonding may beused to produce a hermetic seal about an electronic or electromechanicalcomponent in a package. One example of this is illustrated in FIGS. 16Aand 16B in which a method of transient liquid phase bonding is used toseal a package 300 for a device 312. In the example illustrated in FIGS.16A and 16B a bond between a base substrate 302, for example, asemiconductor substrate, and a cap substrate 304, for example a glass,sapphire, or semiconductor substrate, is formed with materialstructures, for example, the coated grains disclosed above or thelayered structures disclosed below, capable of forming a transientliquid phase bond between the substrates 302, 304. The TLP materialstructures 308 are deposited on one (or both) of the substrates 302,304, to form a closed geometric shape, for example, the rectangle 306illustrated in FIG. 16A that encloses an area or cavity 310 in which adevice 312, for example, a microelectromechanical system (MEMS) device,a surface acoustic wave (SAW) device, a bulk acoustic wave (BAW) device,or a film bulk acoustic wave (FBAW) device is mounted. The substrates302, 304 are brought together and the TLP material structures 308 areheated to a temperature above the melting temperature of a lower meltingpoint material in the TLP material structures 308. The temperature ofthe TLP material structures 308 is maintained at or above thetemperature above the melting temperature of the lower melting pointmaterial until the materials of the TLP material structures 308 at leastpartially or completely inter-diffuse to form an alloy. The resultingalloy forms a hermetic seal about the area or cavity 310 in which thedevice 312 is mounted.

In some embodiments, as illustrated in FIGS. 17A and 17B, a method oftransient liquid phase bonding may be used to mount a device 322 on asubstrate 320 to form a structure 305. A bond between the substrate 320,for example, a semiconductor substrate or a printed circuit board, andthe device 322, is formed with material structures, for example, thecoated grains disclosed above or the layered structures disclosed below,capable of forming a transient liquid phase bond between the substrate320 and device 322. The TLP material structures 324 are deposited on aportion of an upper surface of the substrate 320 and/or on a lowersurface of the device 322. The substrate 320 and device 322 are broughttogether and the TLP material structures 324 are heated to a temperatureabove the melting temperature of a lower melting point material in theTLP material structures 324. The temperature of the TLP materialstructures 324 is maintained at or above the temperature above themelting temperature of the lower melting point material until thematerials of the TLP material structures 324 at least partially orcompletely inter-diffuse to form an alloy. The resulting alloy forms anelectrically and thermally conductive bond between the device 322 andthe substrate 320.

In some embodiments, for example, as illustrated in FIGS. 18A and 18B,the bond formed between the device 322 and substrate 320 is used to formone or more electrical paths between electrical contacts, for example,bond pads on the device 322 and substrate 320. In such embodiments,instead of covering substantially the entire area between the device 322and the substrate 320 as in FIGS. 17A and 17B, the TLP materialstructures 324 are deposited on a plurality of separated areas on thelower surface of the device 322 and/or upper surface of the substrate320. At least one electrical contact is disposed on the upper surface ofthe substrate 320 and on the lower surface of the device 322 within atleast one of the separated areas.

In some embodiments, the device 312 of FIGS. 16A and 16B may be bondedto the substrate 302 using a method as illustrated in either of FIGS.17A and 17B or FIGS. 18A and 18B. The TLP material structures may thusbe used to form both a hermetic seal for the device 312 in the package300 and for providing electrical communication between electricalcontacts on the device 312 and the substrate 302.

A method of bonding the surfaces of two substrates is illustrated inFIGS. 19-22. FIG. 19 illustrates at 330 a first substrate 332 and asecond substrate 342 that are to be joined. A first layer of gold 334 isdeposited on the illustrated surface of the first substrate 332 and asecond layer of gold 344 is deposited on the illustrated surface of thesecond substrate 342. Surface irregularities, illustrated as pair ofgold bumps 336 a, 336 b are present on the upper surface of the firstlayer of gold 334 opposite the surface of the first layer of gold 334disposed on the illustrated surface of the first substrate 332. Thefirst and second gold layers 334, 344 have thicknesses that may rangefrom between about 10 nm and about 10 μm, although embodiments disclosedherein are not limited to having gold layers of any particularthicknesses.

In FIG. 20 a layer of a bonding material 352, for example, indium, hasbeen added to the lower surface of the second layer of gold 344 oppositethe surface of the second layer of gold 344 disposed on the illustratedsurface of the second substrate 342 to form structure 350. The indiummay be added by a physical or chemical deposition process, a platingprocess, or any other process of metal deposition known in the art.

FIG. 21 illustrates a structure 360, which is formed from structure 350by bringing the substrates together so the bonding material layer 352comes into contact with the first layer of gold 334 and heating thebonding material layer 352 to a temperature at which it melts andconforms to the upper surface of the first layer of gold 334, formingmolten bonding layer 362. The structure 360 is maintained at an elevatedtemperature for a period of time sufficient for gold from the firstlayer of gold 334 and from the second layer of gold 344 and the indiumto inter-diffuse to form alloy bonding layer 372 in structure 370. Theelevated temperature at which the alloy bonding layer is formed is, insome embodiments, above the melting temperature of the indium and belowthe melting temperature of the gold. In other embodiments, the elevatedtemperature at which the alloy bonding layer is formed is below themelting temperature of the indium. The heat is removed upon formation ofthe alloy bonding layer 372.

The method illustrated in FIGS. 19-22 may suffer from disadvantages. Forexample, if the surface of the indium to be bonded to the first layer ofgold 334 is left uncovered and exposed to air it may form a surfacelayer of indium oxide that may interfere with the bonding process.Further, the gold in the second layer of gold 344 may inter-diffuse withthe layer of indium 352 to form a gold-indium alloy prior to the bondingprocess or during heating to the desired bonding temperature, reducingthe amount of unalloyed indium available for forming the desired bond.

Another method of bonding a pair of substrates is illustrated in FIGS.23A-23D. FIG. 23A illustrates the pair of substrates 332, 342 to bejoined. First substrate 332 has a first layer of gold 334 including goldbumps 336 a and 336 b deposited on it, similar to substrate 332 of FIG.19. Second substrate 342 has a second layer of gold 344 deposited on it,similar to substrate 342 of FIG. 19. Second substrate 342 of FIG. 23Aalso has a layer of a bonding material 380, for example, indium,deposited on the second gold layer 344 and a third layer of gold 382deposited on the layer of bonding material. The layer of bondingmaterial 380 of FIG. 23A is thinner than the layer of bonding material352 illustrated in FIG. 20. FIG. 23B illustrates the first and secondsubstrates 332, 342 aligned for bonding.

The third layer of gold 382 deposited on the layer of bonding material380 seals the layer of bonding material 380 from the atmosphere,reducing or eliminating the tendency of the layer of bonding material380 to form a surface oxide. In some embodiments, the third layer ofgold 382 may be at least about 15 nanometers thick to provide acceptablesuppression of oxidation of the surface of the layer of bonding material380. However, room temperature diffusion or diffusion as the structureof FIG. 23B is heated to bonding temperature causes gold from the secondgold layer 344 and from the third gold layer 382 to inter-diffuse withthe material of the bonding layer, forming an alloyed material, forexample, AuIn₂ as illustrated in FIG. 23C. This effect is morepronounced with thinner rather than thicker bonding material layers. Ifthe bonding material layer is too thin, or if inter-diffusion takesplace for too long or at too high a temperature, the entire layer ofbonding material 380 may be alloyed.

The alloy layer 384 formed from the inter-diffusion of the gold andbonding material may have a melting temperature higher than the purebonding material, as is the case in the gold-indium system. The alloylayer 384 thus, in some embodiments, will not melt at the desiredbonding temperature, and as illustrated in FIG. 23D will not flow toconform to the surface of the first gold layer 334. Some interdiffusionmay occur between the alloy layer 384 and the gold bumps 336 a, 336 b,but the alloy layer will not bond to the remainder of the surface of thefirst gold layer 334, rendering the bond between the first and secondsubstrate 332, 334 weak.

FIG. 24A illustrate a configuration of substrates and bonding layerstructures similar to that of FIG. 23A. In FIG. 24A, however, the layerof bonding material 390 is thicker than the layer of bonding material380 in FIG. 23A. In the structure of FIG. 24A the thicker layer ofbonding material 390 may prevent total alloying of the bonding layer. Afirst alloy layer 394 and a second alloy layer 396 may form byinter-diffusion of the material of the layer of bonding material and thesecond gold layer 344 and third gold layer 392, respectively, but alayer of unalloyed bonding material may remain within the bondingmaterial layer as illustrated in FIG. 24B. The unalloyed bondingmaterial melts at the desired bonding temperature and flows about thegold bumps in the first gold layer 334 forming a conformal bond betweenthe substrates 332, 342 as shown in FIG. 24C. The unalloyed bondingmaterial is alloyed during the bonding process by additionalinter-diffusion between the bonding material and the gold layers,resulting in the alloyed layer of bonding material 398 illustrated inFIG. 24C. The resultant bond is stronger than that illustrated in FIG.23D due to the increased contact area between the alloyed bondingmaterial and the first gold layer 334.

A further method and associated structure for bonding a pair ofsubstrates is illustrated in FIGS. 25A-25C. In FIG. 25A the firstsubstrate 332 and first gold layer 334 and the second substrate 342 andsecond gold layer 344 are similar to those illustrated in FIGS. 19, 23A,and 24A. The bonding material layer 400, for example, a layer of indium,is a thin layer similar to the bonding material layer 380 of FIG. 23A.The layer of indium may be only as thick as necessary to not be fullyalloyed prior to reaching a liquid state and/or to produce enough liquidindium to provide conformal coverage over surface irregularities on thefirst gold layer 334. Unlike the structure shown in FIG. 23A, an upperdiffusion barrier layer 402 (also referred to as a “barrier layer”) isdeposited between the layer of bonding material 400 and the second goldlayer 344, and a lower diffusion barrier layer 404 (also referred to asa “barrier layer”) is deposited on the lower surface of the layer ofbonding material opposite the surface on which the upper diffusionbarrier layer 402 is formed. The upper diffusion barrier layer 402 isformed of a material that suppresses or blocks diffusion of gold fromthe second gold layer 344 into the layer of bonding material 400. Thelower diffusion barrier layer 404 is formed of a material that seals thelayer of bonding material from the atmosphere to suppress or eliminateoxidation of the surface of the layer of bonding material 400 that is tobe bonded to the first gold layer 334. The upper diffusion barrier layer402 and the lower diffusion barrier layer 404 are formed of a materialthat does not rapidly inter-diffuse with the material of the layer ofbonding material 400, or at least that inter-diffuses with the materialof the layer of bonding material at a rate slower than that of gold. Thebarrier material and thickness of the upper diffusion barrier layer 402and the lower diffusion barrier layer 404 are chosen appropriately toreduce unwanted low temperature premature alloying of the binary system.In some embodiments, the upper diffusion barrier layer 402 and the lowerdiffusion barrier layer 404 may have thicknesses of about 15 nanometersor more and provide acceptable suppression of diffusion of the componentmaterials of the bonding structure and of oxygen into the bondingmaterial layer 400. In FIGS. 25A and 25B, the upper diffusion barrierlayer 402 and the lower diffusion barrier layer 404 are illustrated asformed from the same material—platinum. In other embodiments, the upperdiffusion barrier layer 402 and the lower diffusion barrier layer 404are formed from different materials. Suitable materials for the upperdiffusion barrier layer 402 and/or the lower diffusion barrier layer 404include, for example, titanium, platinum, nickel, indium oxide, tin, andcombinations thereof.

As illustrated in FIG. 25B as compared to FIG. 24B, as the bondingstructure including the layer of bonding material 400 and the upperdiffusion barrier layer 402 and lower diffusion barrier layer 404 isheated and brought into contact with the first gold layer, prematurealloying of the layer of bonding material 400 is suppressed. Theunalloyed bonding material thus melts and flows about the bumps in thefirst gold layer 334 to form a conformal bond with the first gold layer334. After being maintained at a suitable temperature for a suitabletime to allow for the material of the upper and lower diffusion barrierlayers 402 and 404 and the gold from the first and second gold layers334, 344 to inter-diffuse with the material of the layer of bondingmaterial, the bonded structure of FIG. 25C results. This structureincludes an alloyed bonding layer conformally bonded to both the firstand second gold layers 334, 344.

In accordance with another aspect disclosed herein transient liquidphase bonding is performed with a bonding structure including one ormore stacked films of one or more bonding components as illustrated inFIGS. 26A-26C. The stacked films may be substantially planar. Thestacked films include a multitude of interposed layers of the high andlow melting point materials rather than a single thicker pair of layers.In FIG. 26A, the higher melting point material layers are illustrated asgold layers 412, 416 and the lower melting point layers of bondingmaterial are illustrated as indium layers 410, 414. The amount ofbonding material in each layer of bonding material 410, 414 may be lessthan would be desired to form a conformal bond between a pair ofsubstrates, however, the total amount of bonding material in themultiple layers of bonding material is selected to be sufficient toprovide a conformal bond between substrates. The layers of bondingmaterial (for example, indium) 410, 414 may be only as thick asnecessary to not be fully alloyed prior to reaching a liquid stateand/or to produce enough liquid phase bonding material to provideconformal coverage over surface irregularities on the first gold layer334. The layers 412, 416 of the high melting point material may be onlyas think as necessary to provide sufficient material to fully alloy withthe full quantity of bonding material in the layers of bonding material410, 414.

The bond will happen faster when providing a bonding structure includinga plurality of thinner high melting point material layers and layers ofbonding material instead of a single thicker layer of bonding materialdisposed between layers of the higher melting point material becausediffusion (or inter-diffusion) has to proceed only through thinnerlayers of material to achieve complete alloying of the bondingstructure. Further, in the structure illustrated in FIG. 26A wherehigher melting point material layers (gold layers 344, 412, 416) areprovided on both upper and lower surfaces of the layers of bondingmaterial 410, 414 inter-diffusion of the higher melting point materialand the material of the layers of bonding material 410, 414 proceedsfrom both sides of the layers of bonding material 410, 414. In someembodiments, full alloying of the bonding structure of FIG. 26A mayoccur in as little as between about 10 minutes and 15 minutes at about270 degrees C. This is in contrast with traditional gold-goldthermocompression bonding which may require heating to about 400 degreesC. for about 30 minutes. The bonding structure of FIG. 26A thusintroduces less thermal energy into devices or substrates undergoingbonding resulting in less concern for diffusion of material in theformed devices or substrates that might otherwise reduce the reliabilityof the devices or resultant bonded component.

Another advantage of providing a bonding structure including a pluralityof thinner high melting point material layers and a plurality of layersof bonding material instead of a single thicker layer of bondingmaterial disposed between layers of the higher melting point material isthat thinner layers of low melting point material in the layers ofbonding material will be less likely to “squeeze out” of the desiredbonding area during bonding due to higher viscous forces in thinnerfilms.

As further illustrated in FIG. 26A, in some embodiments, barrier layers418 a, 418 b, 418 c, 418 d are disposed at each interface between thehigh melting point material (the gold layers 344, 412, and 416) and thelayers of bonding material (indium layers 410, 414). The barriermaterial and thickness are chosen appropriately to reduce unwanted lowtemperature premature alloying of the binary system (the gold layers andthe indium layers). The material and thickness of the layers in thebonding structure of FIG. 26A are further chosen to give an appropriaterate of alloying at elevated temperature, for example, at a temperatureat or above the melting point of the low melting temperature material ofthe layers of bonding material. The barrier layers are in variousembodiments formed of one or more of, for example, titanium, platinum,nickel, indium oxide, tin, or combinations thereof.

The layers of bonding material (for example, indium) 410, 414 may beonly as thick as necessary to not be fully alloyed prior to reaching aliquid state and/or to produce enough liquid phase bonding material toprovide conformal coverage over surface irregularities on the first goldlayer 334. The layers 412, 416 of the high melting point material may beonly as thick as necessary to provide sufficient material to fully alloywith the full quantity of bonding material in the layers of bondingmaterial 410, 414. In some embodiments, the barrier layers 418 a, 418 b,418 c, 418 d may have thicknesses of about 15 nanometers or more andprovide acceptable suppression of diffusion of the component materialsof the bonding structure and of oxygen into the bonding material layers420, 424.

As illustrated in FIG. 26B as the bonding structure including the layers410, 412, 414, and 416 is heated and brought into contact with the firstgold layer 334, the layers of bonding material melt and the bondingstructure forms a conformal bond with the first gold layer 334. Theformation of the conformal bond may occur at least in part by the thinlayers of high melting temperature material 412, 416 deforming aboutsurface irregularities such as the illustrated bumps in the first goldlayer 334. Additionally or alternatively, molten material from thelayers of bonding material 410, 414 may flow about surfaceirregularities in the first gold layer 334 to form a conformal bond. Asillustrated in FIG. 26C, the bonding structure is maintained at atemperature and time suitable to form an alloyed bonding layer 418conformally bonded to the first gold layer 334 and the second gold layer344, bonding together these layers and any substrates, devices, orcomponents on which the gold layers 334, 344 are deposited.

FIGS. 27A-27C illustrate how a bonding structure including multiplelayers of high melting temperature material 344, 422 and multiple layersof lower meting temperature bonding material 420, 424, as well asoptional barrier layers 426 a, 426 b, 426 c, 426 d, may form a conformalbond between a second substrate 342 and an upper surface 428 of amaterial layer, for example, first gold layer 334 disposed on firstsubstrate 332, having an irregularity in the form of a step 430 on itsupper surface 428.

FIG. 27A illustrates a second gold layer 344 disposed on a secondsubstrate 342 and on which is disposed a bonding structure havingmultiple layers of high melting temperature material 344, 422, multiplelayers of lower meting temperature bonding material 420, 424, andbarrier layers 426 a, 426 b, 426 c, 426 d disposed at the interfacesbetween the layers of high melting temperature material 344, 422, andthe layers of lower meting temperature bonding material 420, 424. Thisstructure is similar to that illustrated in FIG. 26A, except the lowerhigh melting temperature material layer (gold layer 416) is omitted.

As illustrated in FIG. 27B, as the bonding structure is brought intocontact with the first gold layer 334 and heated, the layer of highmelting temperature material 422 deforms and the molten low meltingtemperature bonding material flows to conformally bond the second goldlayer 344 to the stepped surface of the first gold layer 334 on bothsurfaces 428 and 430, for example, in region 432. As illustrated in FIG.27C, the bonding structure is maintained at a temperature and timesuitable to form an alloyed bonding layer 434 conformally bonded to thefirst gold layer 334 and the second gold layer 344, bonding togetherthese layers and any substrates, devices, or components on which thegold layers 334, 344 are deposited.

In FIGS. 26A and 27A bonding structures including pairs of layers ofbonding material are illustrated. It is to be understood that in otherembodiments, more than two layers of bonding material, for example,layers of indium, separated by layers of higher melting temperaturematerial, for example, layers of gold, and optionally layers of barriermaterial provided between the bonding material and higher melting pointmaterial layers may be provided. For example, in some embodiments threeor more layers of bonding material and associated layers of highermelting temperature material and barrier layers may be provided.

It should be understood that although the structures and methodsdescribed with reference to FIGS. 19-27C were described as being used tobond one substrate to another, these bonding structures and methods areequally applicable to bonding a device or component to a substrate oranother device or component of an electronic system and/or to componentsof a package for an electronic device or system.

In some embodiments, the relative amounts of high temperature meltingpoint material and lower melting point bonding material in the variousmaterial layers in the structures and methods described with referenceto FIGS. 19-27C may be selected such that a final alloyed bonding layeris formed that includes the same relative amounts of high temperaturemelting point material and lower melting point bonding material in thedisclosed bonding structures and has a melting point between that of thelower melting point bonding material and the higher melting pointmaterial. For example, in the embodiment shown in FIGS. 26A-26C, theratio of the total amount of indium in layers 410 and 414 to the totalamount of gold in layers 412 and 416 may be selected such that thealloyed bonding layer 418 has a melting temperature between that ofindium and gold. In some embodiments, the amount of gold in the goldlayers 412, 416 may be selected to be less than that which would providea desired ratio of gold to indium in the final alloyed layer 418 toaccount for additional gold that would diffuse into the alloyed bondinglayer from one or both of the first gold layer 334 and the second goldlayer 344 and provide the desired ratio of indium to gold in the alloyedbonding layer 418.

A method, generally indicated at 500 for forming a bonding structure asdisclosed herein is illustrated in FIG. 28. In act 502 a substrate isprovided. The substrate may include, in various embodiments, a mountingsubstrate, for example, a printed circuit board or a component of apackage for an electronic device or may include a surface of anelectronic device or component. In act 504 a first binary componentlayer is formed on the substrate. The first binary component may be amaterial with a higher melting temperature than a second binarycomponent that will be subsequently deposited. The first binarycomponent layer may be a layer of gold, for example, layer 344illustrated in FIGS. 26A and 27A. Formation of the first binarycomponent layer, as well as the other material layers included in thevarious structures and methods disclosed herein may be accomplished byphysical vapor deposition (sputtering or evaporative deposition),chemical vapor deposition, electroplating, screen printing, or any othermethod of material deposition known in the art.

In act 506 a barrier layer is formed on the first binary componentlayer. The barrier layer may include, for example, titanium, platinum,nickel, indium oxide, tin, or combinations thereof. The barrier layermay be, for example, barrier layer 418 a illustrated in FIG. 26A orbarrier layer 426 a illustrated in FIG. 27A.

In act 508 a second binary component layer is formed on the barrierlayer deposited in act 506. The second binary component layer includesor consists of a material with a lower melting temperature than thematerial of the first binary component layer. For example, if the firstbinary component layer is formed from gold, the second binary componentlayer may be formed from indium. The second binary component layer maybe, for example, layer 410 illustrated in FIG. 26A or layer 420illustrated in FIG. 27A.

In act 510 a second barrier layer is formed on the second binarycomponent layer deposited in act 508. The second barrier layer may besimilar or the same in terms of material and/or thickness as the barrierlayer deposited in act 506. The second barrier layer may be, forexample, barrier layer 418 b illustrated in FIG. 26A or barrier layer426 b illustrated in FIG. 27A.

In act 512 another (a second) first binary component layer is formed onthe second barrier layer. The another first binary component layer maybe similar or the same in terms of material and/or thickness as thefirst binary component layer deposited in act 504. The another firstbinary component layer may be, for example, layer 412 illustrated inFIG. 26A or layer 422 illustrated in FIG. 27A.

In act 514, a third barrier layer is formed on the another first binarycomponent layer. The third barrier layer may be similar or the same interms of material and/or thickness as the barrier layer deposited in act506. The third barrier layer may be, for example, barrier layer 418 cillustrated in FIG. 26A or barrier layer 426 c illustrated in FIG. 27A.

In act 516, another (a second) second binary component layer is formedon the barrier layer deposited in act 514. The another second binarycomponent layer may be similar or the same in terms of material and/orthickness as the second binary component layer deposited in act 508. Theanother second binary component layer may be, for example, layer 414illustrated in FIG. 26A or layer 424 illustrated in FIG. 27A.

In act 518, a fourth barrier layer is formed on the another secondbinary component layer. The fourth barrier layer may be similar or thesame in terms of material and/or thickness as the barrier layerdeposited in act 506. The fourth barrier layer may be, for example,barrier layer 418 d illustrated in FIG. 26A or barrier layer 426 dillustrated in FIG. 27A.

FIG. 29 illustrates a flowchart of another method, indicated generallyat 520, of forming a bonding structure. Acts 522, 524, 526, 528, 530,532, 534, 536, and 538 of the method of FIG. 29 correspond to acts 502,504, 506, 508, 510, 512, 514, 516, and 518, respectively of the methodof FIG. 28. The method of FIG. 29 specifically indicates that thematerial of the first binary component layers is gold and the materialof the second binary component layers is indium. The barrier layers ofthe method of FIG. 29 may be similar or identical in terms of materialsand thicknesses as the barrier layers in the method of FIG. 28.

FIGS. 30 and 31 illustrate flowcharts of methods, indicated generally at540 and 560, respectively of bonding a first assembly to a secondassembly. In some embodiments, one or both of the first and secondassemblies include a substrate, for example, a semiconductor substratethat may include active devices, a printed circuit board, or a componentof a package for an electronic device. In other embodiments, one or bothof the first and second assemblies include an electronic device, adevice package, and/or other components of an electronic system. Thefirst and second assemblies are not limited to being of any particulartype.

In act 542 of method 540 a first assembly having a first binarycomponent layer on a substrate is provided. The first binary componentlayer is in some embodiments a layer of gold (see act 562 of method560). In act 544 of method 540 a second assembly having a plurality ofbinary layers on a substrate is provided. Act 544 may include sub-steps,for example, one or more of acts 502-518 or acts 522-538 of methods 500and 520, respectively, for forming the plurality of binary layers. Theplurality of binary layers is in some embodiments a structure includinga plurality of gold and indium layers (see act 564 of method 560, andthe structure illustrated in FIGS. 26A and 27A).

In act 546 of method 540 and act 566 of method 560, the second assemblyis positioned against the first assembly. In act 548 of method 540 thefirst and second assemblies are heated to a temperature that is greaterthan the melting point of the second binary component but less than themelting point of the first binary component. In some embodiments, thetemperature is greater than the melting point of indium but less thanthe melting point of gold (see act 568 of method 560).

In act 550 of method 540 the temperature of the assemblies is maintainedto facilitate inter-diffusion of the first binary component and secondbinary component to form an alloy from the first binary component andthe second binary component. In some embodiments, the alloy is formedfrom inter-diffusion of gold and indium (see act 570 of method 560).

Variability in a manufacturing process including TLP bonding may affectthe quality of bonds formed with the materials used to form a TLP bond.In some embodiments, a desired final bond is formed from an amount of alower melting point material, for example, indium, and an amount of ahigher melting point material, for example, gold that results in theformation of a conformal bond over a substrate wherein the alloyedbonding material is a stoichiometric intermetallic alloy of the firstand second materials, for example AuIn₂. As the term is used herein, astoichiometric intermetallic alloy is one having a formula A_(a)B_(b),where A and B are metals and both a and b may be expressed as wholenumbers. Stoichiometric intermetallic alloys may also include ternaryalloy systems with formulas A_(a)B_(b)C_(c) where each of A, B, and Care metals and each of a, b, and c may be expressed as whole numbers.Stoichiometric intermetallic alloys may also include alloys with morethan three metal components.

A bond formed from an amount of a lower melting point material, forexample, indium, and an amount of a higher melting point material, forexample, gold that results in the formation of a conformal bond over asubstrate wherein the alloyed bonding material is a stoichiometricintermetallic alloy of the first and second materials is illustrated in,for example, FIG. 24C and FIG. 27C. If there is too little of the lowmelting point material, the resulting bond element may resemble thatshown in FIG. 23D, where there was an insufficient amount of low meltingpoint material to flow about the surface imperfections 336 a, 336 b inthe lower substrate 334, rendering the final bond non-conformal to thelower substrate, and thus weaker than the bond illustrated in FIG. 24Cor FIG. 27C. If there is an excess amount of the low melting pointmaterial, a phase including a higher amount of the lower melting pointmaterial, for example, having an amount greater than that of astoichiometric intermetallic alloy, may remain in the finished bond.This is illustrated in FIG. 32. In FIG. 32, there is an excess amount ofindium 805 in the bond element prior to bonding, or alternatively, notenough gold in gold layers 810 a, 810 b, and 810 c to form the AuIn₂intermetallic throughout the entire bonded element 815 during bonding.As a result, the bonded element 815 includes an indium rich layer 825disposed between layers of AuIn₂ intermetallic 820. The indium richlayer 825 has a lower melting temperature than the layers of AuIn₂intermetallic 820, so the indium rich layer 825 could melt and reflowduring subsequent processing of a device or package including the bondedelement 815, potentially causing a failure of the bonded element 815 ormigration of indium into undesired locations, potentially resulting inreliability issues.

To guard against process variations and/or an off target process thatmay result in non-ideal bonding elements, such as those illustrated inFIG. 23D or FIG. 32, to be the sole forms of bonding elements present ina bonded device or package, one may intentionally form redundant bondingelements with different ratios of low melting point material to highmelting point material. Even with process variability, one of theredundant bonding elements would be likely to have a structure similarto the desired structure illustrated in FIG. 24C or FIG. 27C, includinga conformally formed stoichiometric intermetallic alloy, even if one ormore of the other bonded elements had less desirable structures, forexample, as illustrated in FIG. 23D or FIG. 32.

A bonding element having an intentionally higher amount of availablehigher melting point material than necessary (given an “on-target”process) to form a stoichiometric alloy with a lower melting pointmaterial may be formed in various manners. In a first example, asillustrated in FIG. 33A, bonding material elements may be formed with astructure 830 including an excess volume of the higher melting pointmaterial 810 relative to a volume of the lower melting point material805 in a complimentary structure 835. A bonded element 840, formed byinterdiffusion of the materials in structures 830 and 835, may have anexcess amount of the higher melting point material 810 than thestoichiometric alloy. The resultant alloy may be non-stoichiometric withan excess amount of the higher melting point material (for example,AuIn_((x<2)) as illustrated in FIG. 33A). In various embodiments, thestructures 830, 835 may be in the form of elongate structures, asillustrated in FIG. 33B, or in the form of circular structures, asillustrated in FIG. 33C, or combinations thereof. In some embodiments,the structures illustrated in FIG. 33C may be appropriate for use whenthe bonded element 840 is intended to be used to form an electricalcontact with a device.

A bonding element having a proper or approximately proper amount ofavailable higher melting point material (given an “on-target” process)to form a stoichiometric alloy with a lower melting point material maybe formed in various manners. In a first example, as illustrated in FIG.34A, bonding material structures having a structure 845 including thehigher melting point material 810 may include a sufficient volume of thehigher melting point material 810 relative to a volume of the lowermelting point material 805 in a complimentary structure 850 so that theresultant bonded element 855, formed by interdiffusion of the materialsin the structures 845, 850, has a proper or approximately proper amountof the higher melting point material 810 to form the bonded elementsubstantially or fully of the stoichiometric intermetallic alloy. Invarious embodiments, the structures 845, 850 may be in the form ofelongate structures, as illustrated in FIG. 34B, or in the form ofcircular structures, as illustrated in FIG. 34C, or combinationsthereof. In some embodiments, the structures illustrated in FIG. 34C maybe appropriate for use when the bonded element 855 is intended to beused to form an electrical contact with a device. In FIG. 34C, structure845 has substantially the same diameter as structure 850 and is locatedbeneath structure 850 and is thus not visible.

A bonding element having an intentionally lower amount of availablehigher melting point material than necessary (given an “on-target”process) to form a stoichiometric alloy with a lower melting pointmaterial may be formed in various manners. In a first example, asillustrated in FIG. 35A, bonding material elements may be formed with astructure 860 including the higher melting point material 810 present inan amount that is insufficient relative to an amount of the lowermelting point material 805 in a complimentary structure 865 so that theresultant bonded element 870, formed from interdiffusion of thematerials in the structures 860, 865, may not form the stoichiometricintermetallic alloy in the entirety of the bonded element 870. Asillustrated in FIG. 35A, the bonded element 870 may have one or moreportions including the stoichiometric intermetallic alloy 875 and one ormore portions 880 including material richer in the lower melting pointmaterial 805 than the stoichiometric intermetallic alloy 875. In variousembodiments, the structures 860, 865 may be in the form of elongatestructures, as illustrated in FIG. 35B, or in the form of circularstructures, as illustrated in FIG. 35C, or combinations thereof. In someembodiments, the structures illustrated in FIG. 35C may be appropriatefor use when the bonded element 870 is intended to be used to form anelectrical contact with a device.

In other embodiments, the relative amounts of the lower melting pointmaterial and the higher melting point material in a TLP bond may becontrolled by selection of a distance between adjacent bond elements.During bonding, the lower melting point material and the higher meltingpoint material diffuse only a finite distance and thus only materialwithin a certain distance of a TLP bonding structure may be availablefor interdiffusion with the material of the TLP bonding structure. Forexample, FIGS. 36A and 36B illustrate a pair of bonding structures 885including the lower melting point material 805 that are spaced close toone another on a film 890 of a higher melting point material 810 towhich they are to be bonded. The bonding structures 885 are spacedsufficiently close that there is an insufficient amount of the highermelting point material 810 in the film 890 within a distance over whichthe lower melting point material 805 and the higher melting pointmaterial 810 may interdiffuse during bonding to form the stoichiometricintermetallic alloy within the entirety of the bonded elements 895. Thebonded elements 895 thus include portions 900 that are richer in thelower melting point material than the stoichiometric intermetallicalloy. In another bonding structure 905 including the lower meltingpoint material 805 that is spaced further from adjacent bondingstructures than bonding structures 885, a sufficient amount of thehigher melting point material 810 may be available in the film 890within a distance short enough for the lower melting point material 805and the higher melting point material 810 to inter-diffuse duringbonding to form the stoichiometric alloy within the entirety orsubstantially the entirety of the bonded element 910.

In some embodiments, a plurality of TLP bonding layer elements, at leasttwo of which have different target ratios of a lower melting pointmaterial to a higher melting point material, may be used to provideredundant sealing of an area about a device. For example, a devicepackage similar to that shown in FIGS. 16A and 16B may be provided withmultiple TLP bonding elements 308 forming closed shapes, for example,rings or rectangles about a device to form a hermetically sealed cavityabout the device 312. An example of this is illustrated in FIGS. 37A and37B. As illustrated, package 300′ includes three rectangular TLP bondingelements 306A, 306B, and 306C surrounding the device 312. At least twoof the elements 306A, 306B, and 306C have different ratios of a lowermelting point material to a higher melting point material. For example,innermost TLP bonding element 306A may have a target ratio of a lowermelting point material to a higher melting point material, for example,indium to gold, that results in the element 306A forming a bondedelement fully composed of stoichiometric intermetallic alloy, forexample, AuIn₂. One of elements 306B and 306C may have a greater ratioof the lower melting point material to the higher melting point materialthan element 306A and the other of the elements 306B and 306C may have alower ratio of the lower melting point material to the higher meltingpoint material than element 306A. If the process for forming the TLPbonding elements 306A, 306B, and 306C is on target, element 306A willform a bonded element consisting of a stoichiometric intermetallic alloyhermetically sealing the device 312 in the cavity 310. If themanufacturing process is slightly off target and more or less than adesired amount of one of the lower melting point material and the highermelting point material are deposited such that the ratio of thesematerials in structure 306A is not what is desired, one of elements 306Bor 306C may be closer to having the desired ratio of the lower meltingpoint material and the higher melting point material and will form astrong bonding structure to hermetically seal the device 312 within thecavity. Although three TLP bonding elements are illustrated in FIGS. 37Aand 37B it is to be appreciated that more than three or less than threeTLP bonding elements may be utilized in different embodiments.

In TLP bonding elements that are rich in the low melting point material,the low melting point material may have a tendency to flow outward fromthe TLP bonding element during the bonding process. Further, in TLPbonding elements that are rich in the low melting point material, thebonded element may include portions that are rich in the lower meltingpoint material, and that may have a lower melting point than theremainder of the bonded element and may melt and flow during operationor further processing. It may be desirable to form TLP bonding elementswith one or more features that discourage the flow of molten lowermelting point material onto or toward undesirable locations, forexample, toward a device in a package or a bonding pad where the moltenmaterial may interfere with the operation of the device. In someembodiments, for example, as illustrated in FIG. 38, a bonding elementincluding a portion 885 including layers of a higher melting pointmaterial 810 a, 810 b (for example, gold) and a lower melting pointmaterial 805 (for example, indium), and a portion 890 including a layerof the higher melting point material 810 c is provided with a protrusion810 d of the higher melting point material. The protrusion 810 d isillustrated on the top of portion 890, but may alternatively oradditionally be provided on the bottom of layer 810 b. When the portions885 and 890 are brought together and heated, the lower melting pointmaterial melts and inter-diffuses with the higher melting point materialto form the bonded element 895. If the bonding element had more of thelower melting point material than necessary to form a stoichiometricintermetallic alloy (for example AuIn₂) in the entirety of the bondedelement 895, the bonded element may include a portion 900 of thestoichiometric intermetallic alloy, and portion 905 richer in the lowmeting point material than the stoichiometric intermetallic alloy. Theprotrusion 810 d facilitates directing flow of molten lower meltingpoint material during bonding and/or portions of the portion 900 thatmay melt during operation in a predefined direction out of the bondedelement 895 while being formed or after formation. The protrusion 810 dprovides an additional source of the higher melting point material thatmay inter-diffuse with excess lower melting point material where theprotrusion 810 d is present to form the stoichiometric intermetallicalloy where or about a region where the protrusion 810 d is present. Theprotrusion 810 d may thus seal a side of the bonded element 895 so nomolten material may escape from the sealed side. Molten material thuspreferentially or exclusively may escape from the bonded element 895from a side opposite that where the protrusion 810 d is present, forexample, in the direction of arrow A in FIG. 38. Devices, bond pads, orother structures that should be protected from contact with moltenmaterial from the bonded element during bonding and/or during operationmay be positioned on a side of the bonded element 895 opposite from theside from which molten material may preferentially or exclusivelyescape.

For example, in the device package illustrated in FIGS. 37A and 37B, theTLP material elements 306A, 306B, and 306C may be formed similar to thebonding element of FIG. 38 with a preferential direction of escape ofany molten material from the TLP bonding elements 306A, 306B, and 306Cbeing toward another one of the TLP bonding elements 306A, 306B, and306C. The TLP bonding elements 306A, 306B, and 306C thus may serve tocontain any molten material escaping from the TLP bonding elements 306A,306B, and 306C between one another. For example, TLP bonding element306A may be configured so that any molten material from element 306Awill flow toward element 306B, rather than toward device 312. Further,the device package 300′ may be provided with one or more TLP struts 306D(not shown in FIG. 37B) bridging the area between one or more of TLPbonding elements 306A, 306B, and 306C to provide further containment ofany molten material that may escape from any of the TLP bonding elements306A, 306B, and 306C.

In another embodiment, a bond pad or contact of a device may be providedwith multiple TLP bonding elements, or with regions of a TLP bondingelement having different ratios of a higher melting point material (forexample, gold) to a lower melting point material (for example, indium).For example, as illustrated in FIG. 39, a contact 910 of a device may beprovided with four regions 915 a, 915 b, 915 c, 915 d of TLP bondingelement, at least two of which have different ratios of a higher meltingpoint material to a lower melting point material. At least one of theregions 915 a, 915 b, 915 c, 915 d may have a target ratio of the highermelting point material to the lower melting point material that wouldresult in the entirety or sufficiently the entirety of the regionforming a stoichiometric intermetallic alloy (for example AuIn₂) afterbonding. At least one other of the regions 915 a, 915 b, 915 c, 915 dmay have a target ratio of the higher melting point material to thelower melting point material less than that sufficient for the entiretyof the region to form the stoichiometric intermetallic alloy afterbonding. At least another of the regions 915 a, 915 b, 915 c, 915 d mayhave a target ratio of the higher melting point material to the lowermelting point material higher than that sufficient for the entirety ofthe region to form the stoichiometric intermetallic alloy after bonding.Thus even if the process of forming the regions 915 a, 915 b, 915 c, 915d was off target, for example, depositing an excess or a less thandesired amount of one of the lower melting point material or the highermelting point material, it would be likely that at least one of theregions 915 a, 915 b, 915 c, 915 d would have a ratio of the lowermelting point material to the higher melting point material to form abonding/contact element consisting entirely or sufficiently entirely ofthe desired stoichiometric intermetallic alloy. The structure of FIG. 39may additionally or alternatively be utilized for bonding of onesubstrate, for example, a wafer, to another and/or to adhere portions ofa device package to one another. It should be appreciated that thestructure of FIG. 39 may include more or less than four differentregions of TLP bonding element and the regions may be shaped differentlythan illustrated, for example, as strips, discs or any other desiredshape.

It should be appreciated that any of the TLP bonding elementsillustrated in FIGS. 32-39 may include any of the structures discussedpreviously, for example, the multilayered structures of any of FIG. 24A,25A, or 26A or the stepped structure of FIG. 27A and may be included ina device as illustrated in FIGS. 40 and/or 41, described below.

FIG. 40 illustrates an embodiment of an electronic module that may beformed by a method including one or more of the structures and methodsdisclosed herein. The module 600 includes a substrate 602 on which isformed a radio frequency (RF) circuit 604. The RF circuit may be, forexample, a filter or a duplexer. At least one device 606 is sealed orbonded to a portion of the RF circuit utilizing a TLP bonding or sealingmethod in accordance with methods disclosed herein. In some embodiments,electrical connections are made between contacts on the device 606 andcontacts in the RF circuit with a TLP bonding method as disclosedherein, for example, as described with reference to FIGS. 18A and 18B.In other embodiments, the device 606 may be hermetically sealed using aTLP sealing method as disclosed herein, for example, with reference toFIGS. 16A and 16B.

FIG. 41 illustrates an embodiment of wireless device 700 that may beformed by a method including one or more of the boding elements andmethods disclosed herein. The wireless device includes componentsincluding a user interface 702, a memory 704, a baseband sub-system 706,a power management sub-system 708, a transceiver 710, a power amplifier712, an antenna switch module 714, a low noise amplifier 718 and anantenna 720. Any one or more of these components may be bonded to orsealed on a substrate of the wireless device utilizing an embodiment ofa TLP bonding or sealing element and method disclosed herein. In someexample, some of the components of the wireless device 700, for example,one or more of the power amplifier 712, antenna switch module 714, andlow noise amplifier 718 are included in a module 600 as illustrated inFIG. 32, or alternatively may be the device 606 sealed and/or bonded tothe RF circuit 604.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled,” as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Additionally, the words “herein,” “above,” “below,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Detailed Description using thesingular or plural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or acts are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingcomponents, in a different order, and some processes or components maybe deleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or components may be implemented in a variety ofdifferent ways. Also, while processes or acts are at times shown asbeing performed in series, these processes or acts may instead beperformed in parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Anyfeature described in any embodiment may be included in or substitutedfor any feature of any other embodiment. Such alterations,modifications, and improvements are intended to be part of thisdisclosure, and are intended to be within the scope of the invention.Accordingly, the foregoing description and drawings are by way ofexample only.

What is claimed is:
 1. A bonding element comprising: a first transientliquid phase structure including a first material and a second material,the first material having a higher melting point than the secondmaterial, a ratio of a quantity of the first material and the secondmaterial in the first transient liquid phase structure having a firstvalue; and a second transient liquid phase structure including the firstmaterial and the second material, a ratio of a quantity of the firstmaterial and the second material in the second transient liquid phasestructure having a second value different from the first value.
 2. Thebonding element of claim 1 further comprising a third transient liquidphase structure including the first material and the second material, aratio of a quantity of the first material and the second material in thethird transient liquid phase structure having a third value, the thirdvalue being between the first value and the second value.
 3. The bondingelement of claim 1 wherein one of the first value, the second value, andthe third value is selected such that one of the first transient liquidphase structure, the second transient liquid phase structure, and thethird transient liquid phase structures forms an intermetallic alloyhaving a melting point higher than a melting point of the secondmaterial responsive to being heated above the melting point of thesecond material.
 4. The bonding element of claim 1 wherein the firsttransient liquid phase structure is disposed on a substrate andsurrounds a device disposed on the substrate.
 5. The bonding element ofclaim 4 wherein the second transient liquid phase structure surroundsthe first transient liquid phase structure.
 6. The bonding element ofclaim 5 further comprising at least one transient liquid phase strutconnecting the first transient liquid phase structure and the secondtransient liquid phase structure.
 7. The bonding element of claim 5wherein one of the first transient liquid phase structure and the secondtransient liquid phase structure is configured to direct molten liquidescaping from the one of the first transient liquid phase structure andthe second transient liquid phase structure away from the device.
 8. Thebonding element of claim 5 wherein one of the first transient liquidphase structure and the second transient liquid phase structure isconfigured to direct molten liquid escaping from the one of the firsttransient liquid phase structure and the second transient liquid phasestructure toward the other of the first transient liquid phase structureand the second transient liquid phase structure.
 9. A bonding elementcomprising: a first bonded structure including a first alloy of a firstmaterial and a second material, the first material having a highermelting point than the second material, a ratio of a quantity of thefirst material and the second material in the first bonded structurehaving a first value; and a second bonded structure including a secondalloy of the first material and the second material, a ratio of aquantity of the first material and the second material in the secondbonded structure having a second value different from the first value.10. The bonding element of claim 9 wherein one of the first alloy andthe second alloy is a stoichiometric intermetallic alloy of the firstmaterial and the second material.
 11. The bonding element of claim 10wherein one of the first bonded structure and the second bondedstructure includes a region richer in the second material than thestoichiometric intermetallic alloy.
 12. The bonding element of claim 9hermetically sealing a device within a cavity.
 13. The bonding elementof claim 12 wherein the device is a radio frequency (RF) device.
 14. Thebonding element of claim 12 included in a radio frequency (RF) devicemodule.
 15. The bonding element of claim 12 included in a radiofrequency (RF) device.
 16. The bonding element of claim 9 disposed on acontact pad of a device and providing an electrical connection from anexternal circuit to the contact pad.
 17. An electronic device includingat least one component bonded to a substrate with the bonding element ofclaim
 9. 18. The electronic device of claim 17 including at least oneelectrical contact in electrical communication with an electricalcontact of the substrate via the bonding element of claim
 9. 19. Amethod of forming a wireless module including a device and a substrate,the method comprising: forming a first bonding element on a surface ofone of the device and the substrate, the first bonding element includinga first alloy of a first material and a second material, the firstmaterial having a higher melting point than the second material, a ratioof a quantity of the first material and the second material in the firstbonding element having a first value; forming a second bonding elementon a surface of one of the device and the substrate, the second bondingelement including a second alloy of the first material and the secondmaterial, a ratio of a quantity of the first material and the secondmaterial in the second bonding element having a second value differentfrom the first value; contacting the device with the substrate with thefirst bonding element and the second bonding element disposed betweenthe device and the substrate and in contact with both the device and thesubstrate; and heating the first bonding element and the second bondingelement at a temperature and time sufficient for the first material andthe second material in the first bonding element and the second bondingelement to interdiffuse and form a first bonded element and a secondbonded element.
 20. The method of claim 19 wherein the device is one ofa power amplifier, a low noise amplifier, and an antenna switch module.21. The method of claim 19 wherein the ratio of the quantity of thefirst material and the second material in the first bonded element isdetermined by a distance between the first bonded element and a thirdbonded element.
 22. A method of forming at least one bonding structure,the method comprising: forming a first bonding element on a firstportion of the substrate, the first bonding element including a firstmaterial and a second material, an amount of the first material and anamount of the second material being present in the first bonding elementin a first ratio; forming at least one second bonding element on asecond portion of the substrate, the at least one second bonding elementincluding the first material and the second material, the amount of thefirst material and the amount of the second material being present inthe at least one second bonding element in a second ratio different fromthe first ratio; and heating the first bonding element and the at leastone second bonding element to form the at least one bonding structure,the at least one bonding structure consisting essentially of asubstantially stoichiometric alloy of the first material and the secondmaterial.
 23. The method of claim 22 wherein forming the first bondingelement includes forming the first bonding element with a protrusion ofa one of the first material and the second material having a highermelting temperature than the other of the first material and the secondmaterial, the protrusion configured to direct molten material from thefirst bonding element toward the second bonding element.